Textile products made from textile quartz, leached silica and silica fibers have been known in some cases for a long time. They are made according to different processes and consist of pure or nearly pure silicon dioxide (Ullmanns Enzyklopadie der technischen Chemie, 4th Edition (1977) Vol. II, pp. 359-374 , Verlag Chemie, Weinheim/Bergstr. and Melliand Textilber. (1989), pp. 629-632).
Depending on processing conditions and on the single fiber length, the following primary fiber types can be distinguished according to Koch P. A.: Faserstofftabellen, Textilglasfasem (Z.ges.Textilind. 69 (1967), pp. 839-846):
filament (elementary fiber), a practically continuous fiber with defined diameter of the single fiber PA1 staple fiber, non continuous fiber with defined diameter of the single fiber. PA1 sliver, consisting of a continuous assembly of slightly bonded staple fibers in a practically parallel arrangement (not or nearly not twisted staple fibers). The sliver has a defined linear density and is the source material of staple fiber yarns and plied yarns.
Linear products made of textile fibers include among others the following:
Textile fibers are processed to linear products such as, e.g., yarns and to areal products such as, e.g., fabrics or braidings; they can be used too for reinforcement of a matrix, e.g., of synthetics for the manufacture of composites.
The so-called quartz glass fibers and filament yarns which have established themselves on the market are manufactured by the rod spinning process formed from a quartz melt at temperatures greater than 2000.degree. C. Considerable technical resources are required, which means that the prices for the corresponding products are relatively high.
It is also possible to leach glass filament yarn and the textile products manufactured therefrom with acids (DE-OS 2 609 419, GP-PS 2094 363). Leached silica products manufactured by this method are used up to 1100.degree. C. As, however, their mechanical properties are very weak, in the case of textiles heavy fabrics around 600-1300 g/m.sup.2 are mainly used. It has not been possible to establish a broad field of application in textile processing of the respective yarns because of these weak mechanical properties.
It has, however, been possible to manufacture silica fibers with excellent properties by a new production method under advantageous conditions, (DE-PS 2 900 990 and DE-PS 2 900 991). A sodium silicate filament yarn with a drawing off speed of at least 30 m/min (in an example at least 350 m/min) is manufactured in a first processing step from sodium silicate solutions by the dry spinning process. This product, which tends to hydrolyze, is transformed to silica fibers by treatment with acid and/or salt solutions containing hydrogen ions at a retention time of 1 to 15 minutes.
DE-PS 2 900 991 does not give details as to the conditions under which the sodium silicate fibers are fed immediately from the dry spinning unit into the treatment bath: due to the different processing speeds and retention times this is not easily understandable from a technical point of view. In the examples quoted in the DE-PS 2 900 991 also, reference is made to the transformation of "yarn pieces of 1 m length" and Patent claims 6 to 9 clearly refer to the product type "fiber" in the sense of staple fiber or fiber short cut. For chemico-physical reasons textile products made of quartz, leached silica and silica fibers can be used up to ca. 1100.degree. C. The DE-PS 2 900 991 quoted does not however report on this.
Since about 1943 textile glass silver has been manufactured in a one stage process by the drum drawing process (DE-PS 715 884, GB-PS 755 626, DE-AS 1 199 935, DE-AS 1 270 748). Glass is melted at 1250.degree. to 1300.degree. C. and drawn by a rotating drum from a bushing at a speed of V.sub.1 up to approx. 50 m/sec. The adjoining continuous glass filaments are scraped off the drum with the additional aid of a flow of air prior to complete rotation on the drum. Over the width of the drum there is a cone-shaped collecting channel; the sliver formed here is pulled out of the pointed end of the collecting channel and wound at a, compared to V.sub.1, low speed of V.sub.2 up to 10 m/sec: "drum drawing process". The linear density (tex) of the sliver can be adjusted among others by the ratio V.sub.1 : V.sub.2.
Prior to the drawing drum maximum 1% textile size is applied to the continuous glass filaments to give among other the textile glass sliver an appropriate drawing force through adhesion. The textile glass sliver produced in this way consists of fibers with a staple length of approx. 50-1000 mm. After twisting, glass staple fiber yarns with a linear density in the range of 125 text to 2000 tex are usually obtained.
Inexpensive textile products made from these glass staple fiber yarns are used, as a substitute for asbestos, for example as sealings or as thermal insulation material at a continuous application temperature up to approx. 300.degree. C. For chemico-physical reasons, products made from glass staple fiber yarns are not suitable for applications above a temperature range of 400.degree.-500.degree. C.
Textile products made from ceramic fiber yarns are used at temperatures above 400.degree.-500.degree. C. (in some cases as a substitute for asbestos). Ceramic fiber yarns are made from, among other raw materials, ceramic fibers of various lengths on well known production units (slivers manufactured on carding machines, and yarns manufactured on ring spinning frames). Apart from technical limitations in processing and application, ceramic fibers, similar to asbestos fibers, are also suspected of causing cancer, due to the fact that their size--some fibers are less than 3 .mu.m in diameter--permits them to enter the lungs easily (Hodgson, A. A., "Alternatives to Asbestos, The Pros and Cons", Critical Reports on Applied Chemistry, Vol. 26, John Wiley & Sons, Chichester, N.Y., 1989).
U.S. Pat. No. 3,760,049 describes a process for continuously manufacturing high temperature resistant oxide filament yarns (continuous fibers, e.g., 3Al.sub.2 O.sub.3 : 1B.sub.2 O.sub.3 : 3SiO.sub.2). Green fibers manufactured by the dry spinning process (V.sub.1 =40-60 m/min) are transported relaxed as loops on a conveyor belt through the furnaces (V.sub.2 =approx. 0.4 m/rain).
Organic constituents, which enable the extrusion through spinnerettes, are removed by thermal decomposition at temperatures up to approx. 1200.degree. C. and the crystalline structure, which determines the strength, is formed.
It is well known that this type of yarn can be used up to 1200.degree. C. and above. The high raw material and processing costs are responsible for the high selling price. The application in high temperature technology is therefore limited. Staple fiber yarns are not known.
Thus there is an urgent need for economical and health compatible inorganic textile slivers and staple fiber yarns which can be processed to a wide range of textile products and which can be used at temperatures above 400.degree.-500.degree. C. while maintaining, at the same time, their good mechanical properties.